The characteristics of internal combustion engines especially externally ignited internal combustion engines are such that under certain conditions they develop certain undesirable vibriations known as knocking. These vibrations, or knockings, may be eliminated by adjusting the timing of the engine. Preferrably such an adjustment should be done automatically while the engine is operating. In order to perform such an adjustment first the knockings per se must be detected via knocking sensors.
Hitherto, a place was located by an holographic testing on the engine housing which produces the vibration characteristic of the knocking of all cylinders. At or in the proximity of this location the knocking sensor was mounted. Such sensors are well-known in the art. One type of knocking sensor is disclosed in the Germany Pat. No. DE-OS30 13 684. However, this is disadvantageous because such a location in many cases, is not very well accessible, so that the mounting of the knocking sensor is difficult to achieve in view of the rather tight spatial conditions in the engine space of motor vehicles. Furthermore, in certain operating ranges, other vibrations may occur which are very similar to the ones of a knocking signal and therefore could be misinterpreted as a knocking signal. A further disadvantage of the mounting of the known device consists in that not all engines of the same series or types have the same resonance characteristics die to the manufacturing tolerances. Therefore, wide band vibration absorbers must be used for the sensors, and the electrical signals must be tuned individually for each motor by means of a small band filter.